Automatic choke mechanism



Jan. 4, 1966 w. w. CHARRON AUTOMATIC CHOKE MECHANISM Filed Aug. 2, 1962W/L L /AM l4. CHARRON INVENTOR A/KM 2 m 4M ATTORNEYS United StatesPatent f 3,227,428 AUTOMATIC CHOKE MECHANISM. William W. Charron,Livonia, Mich., assignor to Ford Motor Company, Dearboru, Mich., acorporation of.

Delaware Filed Aug. 2, 1962, Ser. No. 214,234 2 Claims. (Cl. 261-39)becomes toolean forsustained operation during warm up, the choke valveshould close momentarily to enrich the mixture andpreventenginestalling. Although the aforementioned functions are well understood, thenumerous attempts to provide a choke mechanism that satis factorilyperforms these functions have not been completely successful.

Hunt Patent No. 1,996,245 is illustrative of the types of chokemechanisms that have been employed with varying degrees of success. Ineach of the embodiments of the Hunt patent, a choke valve that tends tobe opened by engine suction is positioned in the induction passage ofthe carburetor. Latching means are provided to maintain the choke valvein a closed position during low tem-. perature engine cranking. When theengine starts the.

latching means yields and allows the choke valve to open for sustainedoperation.

In one of the embodiments of the Hunt patent a perma-v nent magnet isutilized as the latching means for holding the choke valve in a closedposition during engine crank-.

ing. The magnet exerts a small force which tends to close the chokevalve if an overlean mixture causes the engine to stall during warm up.The strength and location of the magnets conventionally employed forthis purpose are not sufiicient, however, to close the choke valve onceit has opened any appreciable extent.

It is, therefore, the principle object of this invention to provide animproved choke mechanism that utilizes magnetic means for latching thechoke valve in a closed position during cranking.

It is a further object of this invention to provide a choke mechanismthat automatically closes the choke valve during warm up to preventengine stalling by enriching an otherwise overlean mixture.

A carburetor embodying this invention incorporates an unbalanced. chokevalve that tends to be opened by engine suction. Magnetic means arejuxtaposed to a portion of the choke mechanism, when the choke valve isin its closed position, for resisting engine suction induced opening ofthe choke valve. Spring means are additionally provided for resistingengine suction induced open ing of the choke valve.

Further objects and advantages of this invention will become moreapparent as this description proceeds, particularly when considered inconjunction with the accompanying drawings, wherein:

FIGURE 1 is a partially exploded perspective view of a portion of acarburetor embodying this invention;

FIGURE 2 is a cross sectional view taken along line 22 of FIGURE 1;

FIGURE 3 is a view in part similar to FIGURE 2 showing the choke valvein another position;

FIGURE 4 is a view in part similar to FIGURES 2 and 3 showing the chokevalve in still another position; and,

FIGURE 5 is a perspective view of a portion of the choke mechanism.

Referring now in detail to the drawings, and in particular to FIGURE 1,there is shown generally at 11 a portion of the carburetor of aninternal combustion engine. The carburetor 11 is of the two stage, fourbarrel type. That is, two primary induction passages (not shown) and twosecondary induction passages 12 and 13 are formed in a main body 14 ofthe carburetor. Throttle valves are positioned in the primary andsecondary induction passages to control the flow of mixture therethroughin a known manner.

An air horn 15 is secured to the main body 14 of the carburetor bythreaded fasteners (not shown). The air horn 15 defines inductionopenings above the secondary passages 12 and 13 and has a raised portion16 that forms a common induction passage for the primary passages. Achoke valve 17 is pivotally supported within the raised air horn portion16 by a choke shaft 18. The

choke valve 17 is of the unbalanced type. That is, it is on the upperunequal surface area of the choke valve 17 to rotate the choke valve 17into an open position.

The position of choke valve 17 is controlled by an automatic chokeactuating mechanism indicated generally at 19 and shown in exploded viewin FIGURE 1. The automatic choke actuating mechanism 19 includes athermostatic spring 21- secured at one end to a plastic thermostaticspring cover 22. The other end of .the thermostatic spring 21 is coiledas at 23 to receive the projecting end 24 of a thermostatic spring lever25. The thermostatic spring lever 25 is rigidly secured to a bushing 26having an enlarged end 27. A coiled torsional spring 28 encirclesthebushing 26 and is contained between the enlarged end 27 and thethermostatic spring lever 25. A choke housing shaft 29 is rotatablysupported within the bushing 26. Secured to the end of the choke housingshaft 29 is a lever 31 having a plurality of contacts a tang 36 formedupon the thermostatic spring lever 25 and the other end 37 of thetorsional spring 28 contacts one of the tangs 33 formed upon the lever31.

The thermostatic spring lever 25 and the choke housing shaft 29therefore normally tend to rotate as a unit. .The preload on thetorsional spring 28*may bevaried by altering which of the tang-s 33 theend 37 contacts.

The plastic thermostatic spring cover 22 is secured to a choke housing38 by a clamp 39 and a plurality of threaded fasteners 41. The chokehousing 38 is secured upon the carburetor 11 by a plurality of fasteners42 (only one of which is shown) which are threaded into bosses 43 formedintegrally with the main body 14. Mean-s are provided for supplying asource of air heated by the engine to the choke housing 38 andthermostatic spring 21 in a known manner.

When the automatic choke actuating mechanism 19 is secured to thecarburetor 11 as an assembly, a portion of the choke housing shaft 29extends from within the choke housing 38. Nonrotatably secured to thisportion of the choke housing shaft 29 is a lever 44. The lever 44 isfixed axially upon the choke housing shaft 29 Patented Jan. 4, 19661 3by a nut 45 threaded upon the externally threaded end 46 of the chokehousing shaft 29. A lever 47 is nonrotatably secured to the exposed endof the choke shaft 18. A choke valve rod 48 is pivotally connected tothe levers 47 and 44 and transmits motion from the choke housing shaft29 to the choke shaft 18.

A permanent magnet 49 is secured in a sheet metal housing 51 that is, inturn, secured to the raised air horn portion 16 by threaded fasteners52. The permanent magnet 49 is positioned in the periphery of theinduction passage contiguous to the edge of the long end of the chokevalve 17 when the latter is in its closed position (FIG- URE 2). Thechoke valve 17 is formed of a magnetic material and hence is attractedby the permanent magnet 49. The permanent magnet 49, therefore, tends tohold the choke valve 17 in a closed position.

Operation Under low ambient temperatures, the thermostatic spring 21rotates the thermostatic spring lever 25 in a counterclockwisedirection. The motion of the thermostatic spring lever 25 is transmittedto the lever 31 and choke housing shaft 29 through the torsional spring28. This results in counterclockwise rotation of the lever 44 drawingthe choke valve rod 48 downwardly. Downward movement of the choke valverod 48 causes counterclockwise rotation of the choke shaft lever 47 andchoke shaft 18. This moves the choke valve 17 to a closed positionwherein it is attracted by the magnet 49 (FIGURES 1 and 2).

During engine cranking there is insufficient engine suction to cause thechoke valve 17 to open. Once the engine fires and commences running,however, a decrease in pressure occurs below the choke valve 17. Whenthe difference between the pressure below the choke valve 17 and theatmospheric pressure acting upon the choke valve 17 exceeds the forceexerted by the permanent magnet 49 and the preload of the torsion spring28, the choke plate will partially open (FIGURE 3) and permit the engineto run. The lost motion connection provided by the aperture 34 in thethermostatic spring lever 25 and the tang 32 of the lever 31 permitsthis opening of the choke valve 17. An additional load is thereby putupon the torsion spring 28.

If during warm up an overlean mixture tends to cause engine stalling,the pressure on the downstream side of the choke valve 17 will increase(engine suction decreases). The preload of the torsion spring 28 thenovercomes the unbalanced pressure upon the choke valve 17 and moves thechoke valve 17 toward a fully closed position. The attraction of themagnet 49 may cause complete closing of the choke valve 17 if necessaryuntil the engine again runs evenly.

During continued warm up the thermostatic element 21 causes additionalopening of the choke valve 17 (FIG- URE 4). During this stage ofoperation there is less tendency for the engine to stall because of alean mixture. The,trsi0n spring 28 and permanent magnet 49 will,therefore, have less effect upon the position of the choke valve 17.

It should be readily apparent that the combined action of the torsionspring 28 and permanent magnet 49 provided the desired choke action.That is, the choke valve 17 is held closed during engine cranking;however, the choke plate may open to permit sufficient air flow to allowsustained engine operation during warm up. The torsion spring will tendto close the choke valve if an overlean mixture tends to cause enginestalling. The permanent magnet will assist in this operation ifrequired.

It is to be understood that this invention is not limited to the exactconstruction shown and described, but that various changes andmodifications may be made without departing from the spirit and scope ofthe invention.

I claim:

1. A carburetor for an internal combustion engine comprising aninduction passage, a throttle valve positioned in said inductionpassage, a choke valve positioned in said induction passage anterior tosaid throttle valve, said choke valve being unbalanced so that enginesuction tends to open said choke valve, means operably connected to saidchoke valve for moving said choke valve between an opened and a closedposition, spring means operably connected to said choke valve forresisting engine suction induced opening of said choke valve, andmagnetic means supported by said carburetor in said induction passagefor engaging said choke valve when said choke valve is in its fullyclosed position, said choke valve being formed at least in part of amagnetic material whereby said magnetic means resists engine suctioninduced opening of said choke valve.

2. A carburetor for an an internal combustion engine comprising aninduction passage, a throttle valve positioned in said inductionpassage, a choke valve positioned in said induction passage anterior tosaid throttle valve, said choke valve being unbalanced so that enginesuction tends to open said choke valve, thermally responsive meansoperatively connected to said choke valve for moving said choke valvebetween an opened and a closed position in response to temperaturechanges, spring means operatively connected to said choke valve forresisting engine suction induced opening of said choke valve, andmagnetic means supported by said carburetor in said induction passagefor engaging said choke valve when said choke valve is in its fullyclosed position, said choke valve being formed at least in part of amagnetic material whereby said magnetic means resists engine suctioninduced opening of said choke valve.

References Cited by the Examiner UNITED STATES PATENTS 1,996,245 4/1935Hunt 26139 2,158,424 5/ 1939 Hunt. 2,325,918 8/1943 Perrine 261392,818,238 12/1957 Olson 261-39 2,998,233 8/1961 Marsee 26139 HARRY B.THORNTON, Primary Examiner.

HERBERT L. MARTIN, Examiner.

1. A CARBURETOR FOR AN INTERNAL COMBUSTION ENGINE COMPRISING ANINDUCTION PASSAGE, A THROTTLE VALVE POSITIONED IN SAID INDUCTIONPASSAGE, A CHOKE VALVE POSITIONED IN SAID INDUCTION PASSAGE ANTERIOR TOSAID THROTTLE VALVE, SAID CHOKE VALVE BEING UNBALANCED SO THAT ENGINESUCTION TENDS TO OPEN SAID CHOKE VALVE, MANS OPERABLY CONNECTED TO SAIDCHOKE VALVE FOR MOVING SAID CHOKE VALVE BETWEEN AN OPENED AND A CLOSEDPOSITION, SPRING MEANS OPERABLY CONNECTED TO SAID CHOKE VALVE FORRESISTING ENGINE SUCTION INDUCED OPENING OF SAID CHOKE VALVE, ANDMAGNETIC MEANS SUPPORTED BY SAID CARBURETOR IN SAID INDUCTION PASSAGEFOR ENGAGING SAID CHOKE VALVE WHEN SAID CHOKE VALVE IS IN ITS FULLYCLOSED POSITION, SAID CHOKE VALVE BEING FORMED AT LEAST IN PART OF AMAGNETIC MATERIAL WHEREBY SAID MAGNETIC MEANS RESISTS ENGINE SUCTIONINDUCED OPENING OF SAID CHOKE VALVE.